The invention relates to a flat-panel display device comprising an illumination system and a transmission display panel, the illumination system comprising a support, a plate-shaped waveguide and at least one lighthousing accommodating a tubular radiation source for illuminating at least one end face of the waveguide, and a reflector for reflecting radiation emitted by the radiation source towards the waveguide.
The invention also relates to an illumination system and a radiation source suitable for use in such a flat-panel display device.
An illumination system for use in a flat-panel display device of the type described in the opening paragraph is known from the English-language abstract of JP-A 4-141687. In such illumination systems the lifetime of the radiation source is many orders shorter than the lifetime of the display device in which the illumination system is used. Normally, the radiation source is therefore to be replaced several times. A drawback is, however, that the costs of replacing the radiation source are almost as high as the purchase price of a complete display device. In fact, in many cases the radiation source is fixedly connected to the illumination system or to the lighthousing so that the complete lighthousing or illumination system must be replaced. Moreover, there is a risk of damage of the display panel of the display device when the complete lighthousing is replaced and of a non-optimum position of the new lighthousing so that the brightness and homogeneity of the display device are detrimentally influenced.
The illumination system described in said abstract is designed in such a way that, in the case of maintenance of the display device it is sufficient to replace only the radiation source in a simple and relatively inexpensive manner instead of replacing the complete lighthousing or illumination system. The radiation source is situated at the location of the waveguide and at its side remote from the waveguide it is semi-circularly enclosed by, and in direct contact with, a reflector. The reflector is formed as a rotatable plate. When the radiation source is to be replaced, the reflector can be rotated around the axis of the radiation source so that an opening is formed through which the radiation source can be removed in a direction perpendicular to its longitudinal direction and a new radiation source can be installed.
A drawback of the known illumination system is that the reflector is in direct contact with the radiation source so as to keep the radiation source in position, which results in a limitation of the temperature of the radiation source and has a detrimental influence on the lamp properties. Moreover, self-absorption of the radiation source plays an important role due to the limited available free space around the radiation source in the lighthousing. Both drawbacks result in a considerable loss of brightness.
A further drawback in those cases where only the radiation source is replaced is the relative difficulty of optimally repositioning the radiation source with respect to the reflector and the waveguide. In fact, the brightness and homogeneity of the display device are considerably influenced by the position of the radiation source with respect to the waveguide and the reflector.